High Density Interconnected PCBs


In the Printed Circuits Board (PCB) arena, one of the latest and the fastest growing technologies is the High Density Interconnect (HDI) boards. These are multilayer boards offering routing interconnections of extremely high density. Ideal for powering today’s complex devices, these lightweight boards contribute to their high performance. As the electronic industry moves towards shrinking footprints for gadgets, HDI PCBs are the perfect solution for equipment such as smartphones, tablets, laptop computers, and wearable technology represented by virtual reality devices and fitness bands.

Why HDI PCBs

HDI PCBs offer several physical and technical advantages over traditional boards. For instance, even with a lower number of layers, HDI PCBs accommodate a greater number of connections per square unit, leading to PCBs of higher density. Because of the increased capacity of the board, the designer has the advantage of higher flexibility and faster signal processing capability.

HDI PCBs use small, blind vias using the via-in-pad process. The greatly reduced aspect ratio of the vias leads to superior reliability compared to Through-hole PCBs as sustained by IPC studies. This technology offers the use of highly dense and complex packages with extremely low pitch and high pin counts. HDI PCBs meet the demands of OEM for smaller and lighter PCBs with additional functionality. Moreover, with HDI technology, gadgets can have higher signal integrity and improved electrical performance.

Major Benefits

HDI technology allows designers the option to place components on both sides of the PCB. Designers now have more real estate on the PCB, thanks to the technology of blind vias, via-in-pads, and multiple via processes, common in HDI PCBs, which allow them to place increasingly smaller components close together. Decreased component size and pitch also allow designers to place higher number of IO within smaller geometries. Therefore, faster transmission of signals is possible along with a significant reduction in crossing delays and signal losses.

Via-in-Pad Process

Surface mount technology has been progressing fast with the development of CSP, COB, and BGA type packages fitting into increasingly smaller PCB areas. With the via-in-pad process, PCB manufacturers can place vias within the surface of the flat lands. They plate such vias and fill them with either non-conductive or conductive epoxy. After capping and plating, the via-in-pad becomes nearly invisible. Although it seems like a simple activity, special equipment and trained technicians must follow eight different steps to achieve the perfect hidden via.

For instance, PCB manufacturers use the Lenz DLG drill/router with vision drill as a high accuracy drill and route machine. It has a camera system that aligns the holes to be drilled and routed profiles to etched features on the PCB. These machines are extremely accurate drilling machines available in the market, and possess a very precise hole locating capability. This allows producing highly reliable HDI products with reduced annular ring design.

The Lenz DLG has vision assisted drilling capability. This technology allows very precise location of mounting holes with reference to a fiducial or an etched circuit pattern. The routing machine benefits from the vision assistance as it allows features to be routed precisely with reference to the etched circuit pattern on the PCB.

HDI is Cost Effective

As consumer products shrink in size, consumers look for even greater quality, which they grade second only to the price of the item. HDI effectively reduces the price of the PCB, as the technology can reduce an eight-layer through-hole PCB down to a four-layer one, because of the use of microvias. An HDI four-layer PCB can even achieve better functionality than a standard eight-layer PCB can.